The smooth functioning of a long distance telephone communications system depends on the skillful managing of the telephone network and switching offices serving the network. Traffic loads can build up rapidly in portions of a network due to failures in other parts of the network or due to mass calling into a specific area. To insure optimum utilization of facilities it is necessary to monitor, measure and control the flow of traffic in different parts of the network.
Depending on the amount of and direction of traffic flowing between switching offices, one-way or two-way trunk groups may be provided. Two-way trunk groups, of course, offer the advantage of serving traffic in either direction between two offices depending on the demands of the system.
Although it is advantageous to provide two-way trunk groups, these trunk groups suffer from the problem of "glare," a condition which exists when a two-way trunk is simultaneously seized at both ends and neither switching office can utilize the trunk unless the other office releases. Furthermore, two-way trunk groups can be dominated by either end office to the detriment of the other office, unless controls are implemented so that each office can have its fair share of the common trunk group.
In the past, two-way trunk groups have been regulated under the control of a clock so that certain trunks are directionalized, i.e., temporarily made one-way trunks, to serve one office during certain times of the day. An example of one such system is disclosed in U.S. Pat. No. 2,769,864 issued to C. O. Parks on Nov. 6, 1956. While these arrangements are wholly suitable for their intended purposes, they have certain disadvantages. For example, the trunk group is often directionalized based on the history of traffic between the two offices. This history, being a past record, does not reflect the current traffic situation between the offices and does not take into account other traffic situations in other parts of the network which may also affect the traffic between the two offices served by the two-way trunk group.
Also, the calls offered to an interoffice trunk group in a toll network have many different origins and destinations. The probability of a successful completion of a particular call, therefore, depends on what the call's prior routing has been and what its final destination is, in addition to the availability of trunks in the two-way trunk group under consideration.
Accordingly, a need exists for a method and arrangement for dynamically controlling traffic over a two-way trunk group on a call-by-call basis so that calls from one office which have a high probability of completion are routed over the two-way trunk group without degrading traffic flow from the other office sharing the trunk group.